The relevant portions of a corrugator as pertains to the present invention are the double facer machine, a shear knife, a slitter-scorer, a cut-off, a conveyor downstream from the cut-off, a sheet stacker, in that order and drive means for each unit. Upon completion of one production order, it is conventional to sever the web and create a large gap to thereby facilitate adjustments of the slitter-scorer and/or cut-off. The gap is conventionally attained by substantially decreasing the speed of the double facer machine while the web section is processed at the previous speed of the double facer machine. For relevant prior art in that regard, see U.S. Pat. Nos. 2,309,728; 2,764,217; 2,950,658 and 2,985,223.
During any given day, the production order changeover may occur as often as 6 to 7 times. The repetitive acceleration and deceleration of the speed of the double facer machine over a wide speed range with its attendant corresponding changes on the apparatus for controlling transfer of heat to the web is considered to be undesirable from a quality standpoint. More uniform quality is attained if the double facer machine speed remains at a constant.
Since the rate of production of paperboard depends on the speed of the double facer machine, it will be appreciated that substantial decreases in the speed of the double facer constitute a decrease in production. There is an ever-increasing desire to minimize operations which have an undesired effect on production. Another complicating factor not considered by the prior art described in said patents is the present desire to create and maintain a gap in the shingled sheets on conveyors downstream from the cut-off to separate one production order from the next order.
The continuously running corrugator coupled to an automatic sheet stacker does not provide sufficient time on the conveyors to separate the sheets of one order and the different sized sheets of a following order. Not only must there be a gap between the sheets of the two orders but it must be long enough to provide time for the sheet stacker to prepare itself for the new order. A particular problem arises if the corrugator is processing long sheets which could be 20 feet long. When these sheets are ejected onto the slower moving shingling conveyor, a long gap is required to prevent overlapping of the sheets of the two orders and to allow time for the stacker to cycle.
Prior devices try to grab and hold the first sheet of a new production order while the first sheet is on a shingling conveyor. The object of such devices is to prevent not more than three sheets of one production order from being mixed with another production order. That concept of tolerating a small amount of intermixing of production orders is inoperable when the change of the size of the sheets between orders is small or when the change is from a small sheet of 2to 4 feet to a large sheet of 12 to 20 feet.
The problem solved by this invention is how to create a gap to allow time for set up of machines for a new production run and to maintain a separation between production orders while minimizing changes which have an undesirable effect on production or quality.